This invention relates to a sensor used for a so-called electrical heating measurement in which a metal member is inserted in various liquid materials or semi-solid materials, the metal member is heated under the application of electrical current to result in higher temperature than those of said materials, and changes in parameter of the metal member are continuously measured in relation to time lapse to detect changes in state of the materials.
The inventors of this application have already proposed, in Japanese Patent Application No. 58-92079, a measuring method as below. According to this method, in a milk curdling process, a thin metal wire is inserted in milk stored in a tank, an electrical current is passed intermittently or continuously through the thin metal wire for measurement of temperatures of the thin metal wire in relation to time lapse, and a curdy state of milk is judged from a measurement result. In this method, a sensor made of a straight platinum wire of 0.1 mm diameter and 106 mm length is used. The sensor of platinum wire is however disadvantageous in that the platinum wire will be broken when intensively pressed by fingers, that a tank whose interior surface is not applied with insulating treatment will possibly be eroded to perforate under the influence of electrolytic corrosion when the sensor is used for a long time, and that even though the entire length of the sensor is relatively large, a large amount of electrical current is required for heating.